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39 Cards in this Set

  • Front
  • Back
The purpose of a pursuit is to
Maintain object of regard on the fovea
A saccade functions to
Place the object of regard on the fovea rapidly
The vergence system functions to
Align the visual axes to maintain bifoveal fixation
Fast muscle fibers have
Single motor endplates – impulse results in twitch
Slow muscle fibers have
Multiple nerve endings (en grappe) – graded contractions in the absence of muscle action potentials
The longest EOMs are the
Horizontal recti
The thickest EOM is the
Medial rectus
The thinnest EOM is the
Lateral rectus
Hering’s law states that
Two yokes muscles are equally innervated
Vertical movements are around the
X axis
Horizontal movements are around the
Z axis
Torsional movements are around the
Y axis
Sherrington’s law of reciprocal innervation:
When agonists stimulated, antagonists are inhibited
Vestibular ocular reflex (VOR) functions to
Allow eyes to fixate on an object despite head movement
The stimulus to VOR is
Movement of semicircular canals – 3 neuron arc
VOR is faster than the pursuit system
Can track up to 4 HZ –
VOR latency =
15msec
Microsaccades are
Moderately rapid eye movements (2-10deg/sec) 1’-25’ of arc and durations up to 25msec
Microtremors occur at
High frequency (70HZ) – small amplitude
Microdrifts are composed of
Smooth pursuit, vergence and VOR eye movements (slow)
A version is a movement when
The lines of site maintain the same visual angle
Rightward looking is called
Dextroversion
Leftward looking is called
Levoversion
Rotation rightward is called
Dextrocycloversion
Rotation leftward is called
levocycloversion
Smooth pursuits are a
Sloe, steady, involuntary movement that is mediated by a graded response – constant velocity - ~40 deg arc/sec
Latency of smooth pursuits =
125msec
Saccades are
Very rapid eye movements – may reach 1000deg arc/sec – initiated by a burst of nerve impulses
Latency of saccades =
120-160msec
Dynamic overshoots are
A consequence of multiple pulse saccadic movements
Vergence movements have a maximum velocity of
~21 deg arc/sec (slow)
The latency for vergence eye movements is
160msec (twice as fast as that for accommodation)
A dynamic overshoot are present in
Convergence and accommodation – not divergence
Caloric testing for internuclear ophthalmoplegia
COWS cold opposite warm same (pontine gaze mechanism)
Spasmus nutans
- Presents during the first year of life- lasts several months – spontaneously resolves- nystagmus is fine, pendular and rapid- associated with strabismus
Optokinetic nystagmus (OKN)
Induced nystagmus – not dependent on good VA – manifestation of fixation
The most common clinical use of OKN is in the
Diagnosis of parietal lobe disease (disturbance of OKN response in disease affecting the optic radiations)
Blinking proceeds in a
Lateral to medial direction, wiping the cornea clean